Several years ago I read a book called “Why Beautiful People Have More Daughters”  about evolutionary psychology. I really enjoyed how evolutionary psychologists come up with theories about why we behave like we do. One of the main takeaways for me is that it takes our brain takes 10,000 years to evolve. So the things we do today sometimes have their bases in survival in a land 10,000 years ago. This is called the Savanna principle.
For example, 10,000 years ago sweet and fatty foods were not common, but were required for survival because of their high calorie content. So when our 10,000 year old ancestor did come across sweet or fatty foods, those that had a high desire for sweets and fats consumed large amounts, lived longer, and had more kids. Soon our brain evolved to crave sweet and fatty foods, and on the rare occasion when they found a lot of fruit, or a fatty animal was killed, they devoured it. So what happens when our 10,000 year old brain is presented in the last 100 years with cheap and plentiful sweets and fats? We crave it, but since it is so cheap and plentiful, we eat too much, and health problems multiply. In 10,000 years from now, will we have evolved to not like sweets and fats?
The book has a whole chapter on marriage, with a large part of it dedicated to polygamy  . They cite some statistics that show that 83.39% of traditional societies practice polygyny, 16.14% practice monogamy, and only 0.47% practice polyandry. The reason for so little polyandry was that a woman needs a partner that is invested in helping to take care of the child. If the man is not certain the child is his, he has little or no incentive to help. There is no certainty in a polyandrous relationship who the father is.
Side note: as you read on, do not fall for the appeal to nature fallacy. That is tendency to believe what is natural is good. “Natural” means neither good nor desirable.
The idea that humans naturally practice polygyny and have been practicing it for tens of thousands of years comes from an interesting study. Both among primates and non-primate species, the given amount of polygyny in a species highly correlates with the degree of sexual dimorphism in size (i.e. the extent to which the males are larger than the females). The more polygynous a species, the grater the size difference between the sexes. For example, the gibbons are complete monogamous, and there is no difference in size between the sexes. Contrast that to the gorillas, which are extremely polygynous. The males are on average 1.3 times larger than the females. Humans fall somewhere in the middle at 1.1 in height and 1.2 times by weight. As the authors put it
This suggests that, throughout evolutionary history, humans have been mildly polygynous, not as polygynous as gorillas, but not completely monogamous like gibbons either. This is how we know that humans are naturally polygynous.page 86
The authors then go on to postulate that if a society practices monogamy or polygyny it is determined by the women. Monogamy is the norm when many or most women chose to marry monogamously, and polygyny is the norm when many or most the women chose to marry polygynously.
But why would any woman chose polygyny? From the book
One important determinant of the institution of marriage is the degree of resource inequality among men (the difference between the richest men and the poorest men). In societies with a high degree of resource inequality, where rich men are very much richer than poor men, women (and their children) are better off sharing the few wealthy men, because one-half, one-quarter, or even one-tenth of a wealthy man is still better than a whole of a poor man when resource inequality is extreme.page 89
So let’s relate this to Mormon polygyny. With Brigham Young, the most famous and probably prolific polygamist, there was definitely a huge difference in his wealth and the wealth of the common Mormon farmer. Was it better to have 1/50th of Brigham Young’s wealth and attention vice all of a poor farmer living in a mud incrusted cabin? From an evolutionary point of view, was it more likely that a woman’s child would grow to adulthood and reproduce if married to Brigham vice the poor man? Probably so.
How does Joseph Smith factor into this? He does not seems to be much wealthier than his contemporaries. What resource did Joseph possess that was what so much greater that the other men that women would chose polygyny? What about wealth untold in the heavens! Joseph could deliver exaltation! Was it better to have 1/30 of Joseph and live in heaven than a whole man who the women could not be sealed to?
It appears that the Nauvoo polygamy was pretty much based on resource disparity of Godliness (I’m the Prophet and can promise you exaltation), while the Utah polygyny is probably split between the disparity of Godliness and the wealth of the men.
Your thoughts? Could polygamy be awful and repugnantly (which I think it is), and still be natural?
 I have three daughter and no sons, just saying.
 Polygyny = one man/many wives, Polyandry = one woman/many husbands, Polygamy refers to both polygyny and polyandry.